This application requesting 4 years of funding to continue a comprehensive program in the study of genetic susceptibility to seizures. The long term goal of this work is to identify seizure susceptibility genes in inbred mice and use them as the basis for focused studies in humans with common forms of epilepsy. In the initial stages of this project, we used quantitative trait locus (QTL) mapping to study seizure susceptibility in 2 inbred mouse strains: B6, which is resistant to experimental seizures, and D2, which is susceptible. Results of this work identified a locus of major effect, Szs1 (chr.1), and several other loci of moderate effect including Szs11 (chr. 5) and Szs13 (chr. 15). We hypothesize that the genes underlying these loci are fundamentally important in the regulation of neuronal excitability since they were detected consistently in diverse screening paradigms using kainic acid, pentylenetetrazol and electroshock. Thus, over the past funding period, we have focused on characterizing each of these loci further, primarily through a congenic strain-candidate gene strategy. Results have led to nomination of a gene for Szs1 and confirmation of Szs11 and Szs13 in congenic strains. The putative Szs1 gene is Kcnj10 which encodes an inward-rectifying potassium channel and plans to generate formal proof that it is Szs1 comprise the first aim of this proposal. Studies will involve creation of transgenic and knock-in mice and will utilize in vivo and in vitro electrophysiology as well as behavioral tests of seizure susceptibility. Aim 2 involves continued refinement of Szs11 and Szs13 using the prototype strategy we developed for Szs1. Thus, based on completion of congenic strains begun during the last funding period and systematic creation of interval specific congenic strains, we plan to reduce the critical intervals to 3 cM and then begin candidate gene analysis. The third aim involves initiation of new QTL studies designed to exploit the phenotypic diversity exhibited by other inbred mouse strains for identifying seizure susceptibility loci. Overall, we hypothesize that genetic variation associated with seizure susceptibility in mice is related to that which underlies common human epilepsies; and further, that by identifying key loci in mice greater insight will be afforded into mechanisms of seizures and their abolition in humans. Recent data from our lab documenting a significant association between variants of KCNJ10 and idiopathic generalized epilepsy support this concept and justify the continued use of QTL mapping for identifying seizure susceptibility loci in mice.